Use Your Head

I came home from a weekend’s stay with a friend in the countryside most disgruntled at the discovery that her fourteen-year-old son was now taller than I am.

“A full head taller than me!” I declaimed to Holmes. “It’s an embarrassment! I shall have to start wearing shoes with thicker soles to compensate.”

Holmes replied, “Well, Watson, I think you’re wrong to put stock in such things. But here, let us take your mind off it a little. You have put me in a mind of a riddle.”

He then asked me, “What is taller without a head than it is when it has a head on?”

What is the answer?

SOLUTION